Antenna system



July 28, 1953 c. B. H. FELDMAN ANTENNA SYSTEM 4 Sheets-QSl-zeet l FiledJan. 17, 1946 /N VENTOR C. B. H FELDMAN Arron/Er July 28, 1953 c. B. H.FELDMAN ANTENNA SYSTEM 4 Sheets-Sheet 2 Filed Jan. 17, 1946 /NVENTOR CB. H FE/.DMAN

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ATTORNEY July 28, 1953 c. B. H. FELDMAN ANTENNA SYSTEM 4 Sheets-Sheet 5Filed Jan. 17, 1946 /NVENTOR .C B. H FELD/MAN Q .um

A TTORNEV July 28, 1953 c. B. H. FELDMAN ANTENNA SYSTEM Filed Jan. 17,194e 4 Sheets-Shree?. 4

Q @Nk /A/l/EA/oR C B; H FELDMAN ATTORNEY Patented July 28, 1953 ANTENNAsrs'rEM Carl B. H. Feldman, Summit, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication January 17, 1946, Serial No. 641,844

14 Claims. l

This invention relates to an antenna system, l'and particularly to asystem wherein rapid scanning is effected by the movement of a primaryantenna in relation to a passive secondary antenna or fixed parabolicreflector.

In antenna systems where repeated scans of' an exploratory area or angleinvolve the rock- (Cl. Z50-33.63)

1 end to the other of the linear slot facing the reing or oscillation ofa conventional parabolic re- Y flector the mass of the reflector imposesa limitation upon the rate at which the successive scans may be made.The present invention contemplates rapid scanning by the employment of apassive secondary antenna or parabolic or paraboloidal reflector nomovement of which is required in the repetitive movement of the scan-, y

ning beam over a given exploratory angle, the" y sweep of the scanningbeam being effected by the movement of a primary antenna in the form ofan aperture in relation to the focus of a passive secondary antenna orstationary reflector.

The principal object of the invention is to pro"` velocity.

Other objects of the invention include the sev curing of such scanningoperation by the employment of a primary antenna in the form of anaperture adapted to be moved rapidly, successively in the same directionand at uniform velocity across the focus of a passive secondary antenna,and to supply ultra-high frequency wave energy to the aperture withsubstantially unchanged amplitude unaiected by the change in wave pathlength incident to the physical movement of the aperture in relation tothe secondary antenna focus. Conversely, it is an object of theinvention to provide such an antenna lsystem capable of eflicientlyintercepting and conveying to associated receiving apparatus the echoenergy reflected from objects in the exploratory area upon which theradiated energy impinges.

As will be disclosed in the description that follows, these objects areattained, in the specific exemplary structural forms to be described, bypositioning along the latus rectum of a reector Ia wave guide extensioncomprising two coaxial members, one of which is xed and carries alongitudinal linear slot facing the reflector, and the other of which isrotatable and is provided with a helical slot. When the helicallysiotted member iS rotated.. the .intersection ,0I the two iector. Thisaperture, which constitutes a primary antenna, is in communication withthe wave guide through the interior of the coaxial mem- 'bers, travelsthrough the focus of the reflector from one side to the other, andrapidly, continuously, and at a constant velocity repeats this traverseas the helically slotted member continues to rotate. The positionalchange of the aperture along the Wave guide extension constituted by thetWo members is compensated for by one or more associated phase shiftersthat continually operate during the movement of the aperture to maintainunchanged the virtual length of the electrical transmission system oneach side of the aperture, and thus operate to maintain substantiallyconstant energy amplitude at the aperture throughout its movement alongthe wave guide extension.

The antenna system disclosed herein as a preferred form in which theinvention may be embodied will be more fully understood by reference tothe following description taken in conjunction with the drawings, inwhich like reference characters denote the same or similar elef .mentsIn the drawings:

Fig. 1 is a plan view of an antenna structure including the reflector,associated Wave guide,

,. primary antenna and driving mechanism, the reflector being shown insection;

Fig. 2 is a front view of the structure shown in Fig. 1;

Fig. 3 is a sectional end view on line 3-3 of Fig. 2;

Fig..4l shows a longitudinal section of the wave guide extension,including the helically and linearly slotted members, phase lShiftersand driving connections;

Fig. 5 is a plan view of the assemblage of elements shown in Fig. 4;

Figs. 6 and '7 show, respectively, the inner helically slotted and theouter linearly slotted members;

Fig. 8 is a plan view of the primary antenna portion of the wave guideextension including the `slotted members, as seen from the reectortioned views of two elements of the phase shifter;

and

Figs. 12, 13 and 14 show a modified form of moving aperture primaryantenna, Fig. 12 being a plan View partially in section, Fig. 13 a frontview on line 13-13 of Fig. 12 and Fig. 14 a crosssection on line lill 4of Fig. 13.

Referring to the embodiment of the invention illustrated in Figs. 1 to11, inclusive, reference numeral I5 indicates a translation device suchas an ultra-high frequency or centimetric Wave transmitter or receiver,or a radar transceiver, and reference numeral I6 indicates a Wave guideextending to the Wave guide extension l1 forming part of the `antennaproper. If desired, the main wave guide may be provided with rotatablejunctions I8 and I9 so constructed as to permit the antenna proper to beturned in suitably arranged mountings either in a horizontal or avertical plane or both without altering the alignment of a linearlypolarized Wave.

The portions of the antenna structure which cooperate in thetransmission and reception of the ultra-high frequency energy wavesinclude, referring particularly to Fig. 1, the parabolic or parabcloidalreflector 20, the phase shifters 2| and 22 and the slotted members 23,the phase `Shifters and slotted members being rotated by the motor 24through the medium of the drive shaft 25 and gears 26, 21' and 28.

The wave guide extension Vi extends diametrically across and along thelatus rectum -of the paraboloid reiiector 2G and is supported at itsends by the brackets 29. These brackets may also constitute part of thestructural support for Vthe reflector 2S and the driving motor 24.Functionally, the wave guide extension Il terminates at the right-handend of the phase shifter 22. As the parts are represented in thedrawings, the tubular portion of the extension that extends from thispoint to the right-hand bracket 29 serves merely a supporting function.It will be understood that structurally the showing of the varioussupporting elements of the over-all antenna arrangement is somewhatschematic, terminating and strengthening flanges along the sections ofthe outer tube of the wave `guide extension Where the operating elementsare carried, and ball bearings to insure easy rotation of the rotatableparts being omitted for the sake of simplicity in the disclosure of theessential elements of the antenna system.

Proceeding now to a description of the elements of the antenna systeminvolved in the transmission and reception of the ultra-high frequencyenergy waves, theenergy waves passing between the transceiver I5 and theradiating and intercepting aperture 3| flow by way of the wave guide land the inner member of the wave guide extension l1. The waves withwhich the antenna system of the present .invention is designed tooperate are centimetric waves of the Hi type; that is, they are waves ofsuch high fre- .quency as to have a wavelength of only a few centimetersin space, and are waves having a linear electrical polarizationtransverse to the direction of propagation. The direction of the linearelectrical polarization used is indicated by the arrow in Fig. 9 inconnection with the first alternative form of the invention, and by thearrow in Fig. 14 in connection with the second alternative form.

The electrically functioning portion `of the wave guide extension isbest shown in Fig. 4 of the drawing. The outgoing waves pass from theinner member of the Wave guide extension IT through the elements of thephase changer 2l and the interior of the slotted members 23, be-

yond which a portion pass to and are reflected from an end Wall orreccting termination 30 immediately beyond the terminating phase shifter22. This reflecting wall 35 may conveniently be an end wall of theterminating phase shifter 22. The function of the phase shifters 2l and22 in connection with the operation of the longitudinally movableprimary antenna aperture 3l will be described hereinafter.

The slotted members 23 comprise a rotatable helically slotted member anda nxed. or non-rotatable linearly slotted member. Preferably, and asshown, the helically slotted rotatable member designated S2 is the innermember of the two, forming an extension or the inner wave guide channel.The iixed linearly slotted member designated S3 forms a portion of theouter shell or tube of the wave guide extension. rEhe helical slot 3!!is a one-turn slot, and is so out that its two end walls lie in the sameaxial piane of the tubular member 32. Thus the total area of the openingformed by the intersection or" helical slot and linear slot constant at`all times throughout the S60-degree rotation of the helically slottedmember. The aerial length of the linear slot is the same as, or at leastno less than, the axial length ofthe helical slot, the length being suchthat the linear traverse oi the aperture from one end of the slot to theother is equal to an even number of half-wavelengths in the guide.

In the present illustrative embodiment, where asubstantial breadth ofangular scan in azimuth is desirable, the linear traverse of theaperture is equal to seven half-wavelengths (that is, 31/2 wavelengths)in the guide. ln the actual operation of the specic arrangement hereindisclosed a frequency giving a wavelength of 9.32 centimeters or 3.87inches in free space was used. The corresponding wavelength in the guideis 15.8 centimeters or 6.22 inches. Therefore the total l/g-wavelengthtraverse of the aperture Si along the linear slot was 21.77 inches. Withthe elements of the structure disposed along the latus rectum of theparabolic reflector in such a Way that the primary antenna aperture 3|passes through the reflector focus at the midpoint of its traverse, thescanning movement of the directive lobe of the scanning beam isapproximately one degree per inch ol aperture movement. The above isupon the assumption of a principal focal length ior the parabolicreflector of 49 inches.

The connection between the driving motor 24 and the helically slottedmember may con- Veniently be such that the member rotates at the rate of600 revolutions per minute or ten per second. Each complete revolutionof the member 32 causes the aperture 3l to move the entire length of thelinear slot 35, from one end to the other. Assuming the direction ofrotation is clockwise when viewed from the end connected with the mainwave guide, the aperture 3l moves along the linear slot from left toright, as shown in Fig. 8; and as one sweep is terminated at the slotintersection at the right, a new sweep is initiated by the intersectionof the slots at the left in the continuous rotation oi the helicallyslotted member. Thus, the movement or the directive lobe of the antennaconsists of a constantly repeated succession of identical sweeps at aconstant velocity and always in the same direction.

The release of electromagnetic Wave energy from the primary antenna forreflection from the parabolic reflector and propagation into space, is

by way of the outlet or so-called leak constituted by the movingaperture. There is a wellunderstood relation between the contour orrela- Ytive dimensions and location of a wave guide aperture capable ofserving as such a leak, and the direction of electrical polarization ofthe wave in the guide. A circular or rectangular cross-section waveguide having one or more antenna slots, usually one, extending parallelto the longitudinal axis of the guide is conventionally referred to as aleaky pipe or guide of the rst kind, and a circular or rectangularcross-section guide having one or more antenna slots each of the slotsextending in a direction transverse to the longitudinal axis of theguide, and with the array of such slots, if more than one, parallel witheach other and extending in a direction parallel to the longitudinalaxis of the guide is conventionally referred to as a leaky pipe of thesecond kind. For escape of energy through a leak of the first kind, the

Velectrical polarization of the linearly polarized or slot of the outermember 33, thus identifying the structure as a leaky pipe of the firstkind; and by reference to Fig. 14 it may be seen that the axial plane oflinear electrical polarization of the waves in the guide, as indicatedby the arrow, is the same plane in which lies the array of transverseantenna slots (see Figs. 12 and 13) in the outer member 33, thusidentifying the structure as a leaky pipe or guide of the second kind.It may here be noted that in the antenna systems, as shown, theelectrical polarization in spa-ce of the propagated waves in theresultant scanning beam is vertical in the case of a structure such asthat represented by Fig. 9 and is horizontal with a structure such asthat represented by Fig. 14.

Reference will first be made to the nature of the passage of wave energythrough a primary antenna structure of the type shown in Figs. 1 to 9,inclusive. As the helical slot 34 of the inner member 32 from one end tothe other extends through an angle of 360 degrees of revolution andtherefore of orientation with regard to the wave polarization plane,there is always a portion of the length of the slot that, with respectto the passage of linearly polarized waves, forms a leaky pipe of thefirst kind, and another portion that to a less degree forms a leaky pipeof the second kind. This relates merely to the passage of energy betweenthe wave guide interior and the interspace between the tubularconcentric members 32 and 33. As this annular interspace is constantlyin communication with the entire length of the linear slot in the outerslotted member 33, a certain energy leakage may accompany the usefulenergy radiation that takes place at the direct opening from the waveguide dened by the intersection of the two slots. Any such radiatedleakage energy is electrically polarized in the same direction as theusefully radiated energy, and is objectionable; but its radiation may beprevented or substantially reduced by the provision of wave traps suchas those identified by the numerals 36 on the drawings. These wavetraps, most clearly shown on Fig. 9 of the drawings, are long, narrowslot-like chambers extending along and on either side of the linear slotin the outer member. Each of the chambers is disposed in a radial planewith respect to the longitudinal axis of the concentric primary antennamembers. The outer end of each chamber is closed and the inner end is incommunciation with the annular interspace between the two concentricmembers. It has been found by trial that the most effective operation ofthese members as wave traps is secured when each is spaced a distanceapproximately equal to a quarter wavelength in air from the adjacentedge of the linear slot in member 33, and when the depth or radialdimension of each chamber is approximately one-quarter wavelength in airof the wave that is being propagated. The presence of these wave trapssubstantially reduces the amount of leakage energy reaching the linearslot 35 from the interspace between the concentric members.

The shape and area of the primary antenna aperture 3| are determined bythe width of the intersecting slots and the pitch of the helical slot.As actually constructed and operated the breadth of each of the slotswas approximately three-quarters of an inch and the pitch of the helicalslot, as previously stated, was such as to produce one complete turn inan axial distance of 21.77 inches. As a result of this relatively longpitch, the length dimension of the resultant aperture is substantiallygreater than its breadth dimension, and the shape of the aperture is onebetter adapted for use in connection with a leaky pipe of the first kindwhere the linear electrical polarization lies in a plane perpendicularto the plane including the aperture. By modifying the structure,however, it is possible to take advantage of the principle of the leakypipe of the second kind, and thereby discriminate more effective betweenusefully propagated energy from the wave guide and the energy whichescapes through the helical slot into the interspace between theconcentric members.

Such a modified arrangement of the vprimary antenna elements isillustrated in Figs. 12, 13 and 14 of the drawings. As indicated on Fig.13, the one-turn helical slots 31 in member 39 is axially shorter by acertain number of halfwavelengths and of steeper pitch than the helix 34of the modification previously described. The linear slot 38 in theouter concentricvinember 4i! is correspondingly shorter, and theaperture formed by the intersection of the two slots is less elongatedand more nearly square than the aperture formed by the intersection ofthe two slots 34 and 35 in the previously described modification. Wherethe scanning requirements of the associated antenna system are satisfiedby a smaller breadth of aperture movement the length of the one-turnhelical slot may be further shortened and its pitch made still steeper'to approximate more nearly a square shape of Athe aperture formed bythe intersection of the two slots.

With an aperture of this shape it is possible to propagateelectromagnetic waves having a this end, the electromagnetic wavespropagated through the guide are given a linear electrical polarizationoriented to lie in the same axial plane that includes the linear slot ofthe outer member, as indicated by the arrow in Fig. 14, the arrangementthus becoming a leaky pipe of the second kind. The leakage displacementcurrents for Waves which escape from the interior through thelongitudinally extending helical slot and reach the linear slot in theouter member are still polarized perpendicularly to the axis of theconcentric antenna members, and are therefore polarized vertically inspace, and perpendicularly to the horizontal electrical polarization ofthe waves radiated from the aperture formed by the intersection of theslots. It therefore becomes possible to discriminate against suchleakage radiation without aecting the useful and desired radiation.

This is accomplished in the form of the invention illustrated in Figs.12, 13 and 14 by associating with the linear slot 38 and mounting uponthe outer concentric member 4@ a plurality of closely spaced transversepartitions di extending along the slot 38 and perpendicularly thereto.These partitions are terminated in side Walls 42 to form in effect aplurality of wave guides the outer ends of which are open and the innerends of which communicate with the linear slot 38. As the electricalpolarization of the usefully radiated waves is horizontal and parallelwith the axis of the concentric members and the distance between theside walls e?.

is greater than one-half wavelength in space of the radiated frequency,the passing of the energy waves of this polarization is not aected bythe presence of the partitions. But for the vertically polarized leakagewaves the polarization of which is perpendicular to the longitudinalaxis of the concentric members, and therefore in planes parallel withthe planes of the partitions spaced at intervals considerably less andof a depth greater than one-half wavelength in space, these partitionsact as cut-offs to prevent radiation of leakage energy. In other words,the partitioned member comprising the partitions el and the side walls42 is so dimensioned with respect to its plurality of elemental channelsor wave guides as to permit the free passage of usefully radiated waveenergy linearly polarized in the plane of the primary antenna axis, andto act as a cutofi for leakage energy of the same wavelength linearlypolarized in a plane perpendicular thereto. The partitions M are made ofthin metal in order to minimize obstruction to the waves, and are spacedclosely in order to prevent discontinuities in the pattern of thedirective scanning lobe. Obviously, the outer primary antenna member 40of the modification illustrated in Figs. 12, 13 and 14 may also beprovided with the wave traps 3E of the other modification, asillustrated more particularly in Fig. 9, if it is desired further toreduce the passage of leakage energy from the wave guide to the linearslot 38.

Coming now to the matter of the phase Shifters identified generally as2l and 22 on Figs. 1 and 4 of the drawing, it is evident that in thephysical movement of the primary antenna aperture 3i along thelongitudinal slot the length of the electrical transmission systemsupplying energy to the aperture is changed. As the aperture moves fromleft to right along the slot the electrical distance between it and thetransceiver l5 increases and the electrical distance between theaperture and the reflecting wall diminishes.

Consequently, in the absence of means to prevent it, the movement of theaperture would be accompanied by a continual change in amplitude andphase of the radiated energy and a resultant continual change in theelectrical characteristics of the scanning lobe. It is to avoid such aresult as this that the phase Shifters are employed. By their use theelectrical distance from aperture to transceiver and from aperture toreflecting wall is maintained constant at all times during the movementof the aperture.

The phase Shifters that are shown diagrammatically in Fig. 4 and certainelements of which are shown somewhat more clearly in structural detailin Figs. 10 and 11 are of the type disclosed in Patent 2,438,119 grantedon March 23, 1948, to A. G. Fox, and may preferably be modified for widefrequency band operation as disclosed in Patent 2,425,345 granted onAugust l2, 1947, to D. H. Ring. The phase shifter 2| comprises a centralrotatable section or rotor 43 and two end stationary sections M and 45,one of which is a polarizer or circularizer for converting a Wave havinga fixed linear polarization to one having a circular or rotating linearpolarization, and the other of which is a depolarizer or decircularizerfor converting a circularly polarized wave to one having a fixed linearpolarization. The identical end sections function as polarizers ordepolarizers depending upon the direction of Wave propagation in thephase shifter, and therefore upon whether the antenna is transmitting orreceiving high frequency pulses. As shown in Figs. 10 and l1, each ofthe two end sections dii and 45 is provided with two diametral reactancerods i8 spaced apart a distance approximately equal to 3/3 wavelength inthe guide of the wave used, while the rotor 43 has three such diametralrods similarly spaced. The phase shifter 22 comprises two two-rodsections B and 41, section 46 being stationary while section 41 isrotatable. Depending upon the direction of wave propagation each ofthese sections likewise is adapted to operate either as a polarizer oras a depolarizer.

Each of the rotors 43 of phase shifter 2i, and l? of phase shifter 22may be operated to shift the phase angle of the electrical Waves passingthrough it, the rotor 4l shifting the phase angle 360 degrees for eachS60-degree physical rotation of the rotor, while the rotor 43accomplishes the same S60-degree shift of the phase angle by a -degreephysical rotation of the rotor. Therefore in the specic exemplication ofthe invention employing a 9.82 centimeter wave, a 360- degree rotationof rotor 4l or a 18o-degree rotation of rotor 43, producing in each casea phase shift of 360 degrees equal to one wavelength of 6.22 inches inthe guide, increases or diminishes the electrical length of thekcorresponding portion of the transmission system by 6.22 inches.

The longitudinal traverse of the aperture 3| from one end to the otherof the lineal' slot, as previously stated, is 21.77 inches or 31/2wavelengths in the guide. To eiect a corresponding change in theelectrical length of the guide on either side of the aperture thereforerequires 31/2 complete turns of the rotor lll or Ztl/2 half-turns (1%full turns) of the rotor 43 during the time the helically slotted member32 is making one complete turn to move the aperture 3l from one end tothe other of the linear slot 35.

The two rotors 43 and il and the helically slotted member 32 are drivencontinuously and at constant velocity by the motor 2li through thegorizia medium of shaft 25 and the gears 26, 28 and 21, respectively,thek gear ratios being such as to turn the rotor 43 1% turns and therotor 41 31/2 turns, while the helically slotted member 32 is making onecomplete turn. If the phase shifters are so adjusted as to produceappropriate phase angles at the initiation of the 31/2 wavelengthmovement of the aperture along the slot, they will reproduce the sameappropriate phase angles for subsequent repetitions of the aperturemovement because the movement is an exact multiple of thehalf-wavelength.

To change the virtual length of the wave guide on each side of theaperture in the right direction as to lengthening or shortening requiresthe establishment of a denite relation between the direction of rotationof the phase shifter rotor sections and the particular orientation ofthe reactance rods of the stationary phase shifter sections IM, A and l5with respect to the plane of linear polarization of the electromagneticwaves employed. The proper relationship of the various elements for theparticular case in question is indicated in Fig. e. Assuming theelectrical plane of polarization of the waves in the guide to beperpendicular to the plane of the paper and the rotatable elements allarranged to rotate in the same direction, the reactance rods ofstationary sections #lil and 45 are all oriented at the same angle of 45degrees in a clockwise direction (looking into the open left-hand end ofthe wave guide extension) with reference to the linear polarizationplane, and the reactance rods of the stationary section 5.5 are orientedat 45 degrees in a counter-clockwise direction with respect to thelinear plane of polarization. Suppose that the direction of drive of therotors 43 and 41 and of the slotted member 32, with the reactance rodsthus oriented, is in a clockwise direction viewed frorn the left-handend of the wave guide. With these elements thus arranged and with thehelical slot cut as a left-hand thread, the shift of the phase angleproduced by the rotors 43 and 41 is such as electrically in effect tomove the transceiver l5 continuously toward the receding aperture 3l andthe reflecting wall 3l] away from the aperture 3l in exactcorrespondence as to wavelength with the linear movement of the aperturealong the slot, so as at all times to maintain the aperture at anunvarying electrical distance from the transceiver and the reflectingend wall. If the reflecting wall St is a stationary part of thestructure, the linearly polarized electrical vector that rotates withthe phase shifter rotor 41 :also rotates with reference to thereflecting end wall and therefore the end wall must have circularsymmetry. If the reflecting wall 30 forms part of and rotates with therotor 41, then only that portion aligned with the linear electricalvector needs to be reflective.

In effect, the action is such as to keep the aperture throughout itsmovement aligned with a voltage loop of a standing 4wave patternproduced by the interference of the go waves with the return wavesreflected from the end wall 38. As the position of the loops and of thenodes or nulls in this standing wave pattern is purely a function of thedistance in wavelengths to the reflecting wall, a physical recession ofthe wall by an amount exactly equal to the movement of the aperturetoward the wall would cause an energy loop centered on the aperture atthe start of the aperture movement to remain centered on it throughoutits movement. In terms of electrical wavelength between aperture andreflect- 1D ing wall this is the effect of the phase shifter 22. It ineffect moves the reflecting wall backwardly by the same amount and atthe same rate that the aperture moves forwardly. If the impedance matchat the aperture with respect to transmitted energy were perfect, thephase shifter 2l between the aperture and the transceiver would not berequired. The phase shifter 22 between the aperture and the reflectingwall would be all that was necessary to keep the energy loop alignedwith the aperture during the aperture movement. But in practice, it isdiflcult to establish such a degree of impedance match at the apertureas would prevent energy reflection at this point, and therefore thephase shifter 2lV is used to preserve the same impedance at thetransceiver I5.

Obviously, if desired, various combinations of phase shifter elementssuch as disclosed in the previously mentioned Fox Patent 2,438,119, maybe employed to :accomplish the same result as the particular combinationherein set forth. Furthermore, it will be understood that in themodified form of the invention illustrated in Figs. 12, 13 and 14wherein the shorter slots of the slotted members give a shorter traverseof the aperture as measured in wavelengths (specifically 21/2wavelengths) and the electrical linear polarization of the waves isperpendicular to the polarization in the first-described modification,the orientation of the reactance rods in the stationary sections of thephase Shifters and the driving gear ratios for the phase shifter rotorsand the rotating helically slotted member will be correspondinglymodified. Specifically, the gear ratios will be such that the rotor 41makes 21/2 turns and the rotor i3 makes 11/4 turns, while the helicallyslotted member makes one turn. In either form, reversing the directionof rotation of the drive shaft reverses the direction of movement of theaperture along the linear slot without modifying the operation of thesystem.

In accordance with the reciprocity principle, the same arrangement andadjustment of elements of the antenna system employed to give maximumefficiency with respect to the radiated or transmitted waves also givesmaximum eiciency of reception for the waves reflected from objects uponwhich the transmitted wave impinge.

What is claimed is:

1. In combination, a parabolic reflector, a wave guide extending alongthe latus rectum of said reflector and comprising slotted elements theintersection of which forms a primary antenna aperture facing saidreflector and the relative movement of which repeatedly moves saidaperture at a constant rspeed and in the same direction along a lineperpendicular to the reflector axis and including the reflector focus,and means for producing relative movement of said elements.

2. In combinationl a parabolic reflector and a linearly slotted waveguide extension mounted in fixed relation to each other, a helicallyslotted rotatable element coaxially located within said wave guideextension, and means for rotating said element to cause the intersectionof the slots to move repeatedly and in the same direction along thelatus rectum and through the focus of said reflector.

3. In combination, a concave reflector, a wave guide extension lyingalong the latus rectum of said reflector, said extension comprising afixed slotted element and a rotatable helically slotted element forminga primary antenna aperture fac- 1 1 ingr 'said reflector, and meansincluding a motor unit to drive the rotatable element for producingrelative movement of said elements whereby said aperture is movedrepeatedly and in the same direction along the latus rectum and throughthe focus of said reflector.

4. In combination, a passive secondary antenna having 'a principalfocus, a Wave guide extension comprising two concentrically mountedelements, one helically slotted and the other linearly slotted, theintersection of said slots forming an aperture constituting a primaryantenna facing said secondary antenna, and means including a motor driveunit for rotating said h'elically slotted element for causing saidaperture to move unidirectionally, repeatedly and at a uniform speedacross the focus of said secondary antenna.

5. In combination, a parabolic reflector, a wave 'guide extensiondisposed along the latus rectum of lsaiddreflector and having anaperture facing said reflector, means yfor moving said aperture ale'ngsaid extension 'and across the focus of said reflector repeatedly andunidirectionally, and phase shifting means associated with said waveguide extension and operating to compensate for amplitude change due tothe movement of the aperture along the Wave guide extension, thus tomaintain substantially the same amplitude at the aperture during theaperture movement.

6. In combination, aparabolic reflector, a wave guide extension disposedalong the latus rectum of said reflector and terminating in a wave refleeting wall, said Wave guide extension having a movable apertureconstituting a primary antenna facing said reflector, means for movingsaid aperture along said extension and across the focus 'of saidreflector, phase shifting means between sai-:l aperture and said wavereflecting wall, and means for operating said phase shifter in themovement of said aperture to maintain substantially unchanged theelectrical distance between the aperture and the terminal wallthroughout the movement of the aperture along the wave guide extension.

7, In combination, 1a parabolic reector, a wave guide extending from `atransceiver to a Wave reflecting termination forming part of a Waveguide extension disposed 4along the latus, rectum of said reflector, amovable primary antenna aperture formed in said Wave guide extension andfacing said reflector, means for moving said aperture along saidextension and across the focus of said reflector, phase shifting meansincluded in said wave guide between said 'transceiver and said apertureand between said aperture and said Wave reflecting termination, andmeans for operating said phase shifting means in the movement of saidapertureY along "the extension to maintain substantially the saineamplitude at the aperture throughout nthe aperture movement.

3. VIn combination, a parabolic reflector, a wave guide eitensio'nhaving an aperture constituting a primary 'antenna 'facing saidreflector, means for moving said aperture along said 'wave guideextension and across the focus of said reflector, a Wave reflectingtermination at one end of said wave guide extension, a Ytransteive'rconnected With the other end of said extension, and phase shifting'means operated in theinove'ment of said aperture to maintain theaperture throughout its movement at a` substantially unvaryingelectrical distance both from said transceiver and from said refiectingtermination. g Y

9. In combination, a parabolic reflector, a wave guide extension havingan aperture constituting a primary antenna facing said reflector, meansfor moving said aperture along said wave guide extension and across thefocus of said reflector, a wave reflecting Wall at one end of saidextension, a source of ultra-high frequency electrical waves connectedwith the other end of said elif tension, the reflection of Waves fromsaid Wall creating a pattern of standing waves in said extension, andphase shifting means operated inthe movement of said aperture to movesaid standing Wave pattern in correspondence with the aperture movementto maintain an energy loop at said aperture throughout the aperturemovement.

10. In combination, a parabolic reflector, a Wave guide extensionextending along the latus rectum of said reliector, said wave guide'extension including a linearly slotted outer member and a coaxialhelioally slotted rotatable inner member, the aperture formed by theintersection of said slots facing said reflector and constituting aprimary antenna, and means for rotating said inner member to cause saidaperture to move at a uniform speed, repeatedly and in the samedirection across the focus lof said reiiector.

11. In combination, a parabolin reflector, a wave guide extension lyingalong the latus rec'- tum of said reflector, said wave guide extensionincluding an outer member having a linear longitudinal slot and acoaxial rotatable inner mehrber having a ene-turn helical slot, theaperture formed by the intersection of said slots facing said reflectorand constituting a primary antenna, means for supplying ultraehighfrequency linearly polarized electromagnetic 'waves to said Wave guideextensicn, means for rotating said inner member to cause said apertureto move at a luniform speed repeatedly and 'in the same direction acrossthe focus of said reflector, and means disposed along said outer memberin association with said linear for preventing leakage radiation throughsaid slot of energy 'from the interior of said Wave guide extension.

19. In combination, a parabolic reflector, -a wave guide extension lyingalong the latus rectum of said reflector, said `Wave guide extensionincluding an outer 'member hav-ing a longitudinal linear 'slot and acoaxial Arotatable inner mein'- 'ber having a one-turn helical slot, theaperture formed by the 'intersection of said slots facing said'ren'ector 'and constituting-a primary antenna, means for 'rotating saidinner member to cause said 'aperture to move at -a uniform fspee'drepeat edly 'and in the same direction across 'the focus of saidreflector, means for supplying ultra-high frequency linearly polarizedelectromagnetic waves to said extension, the Aelectrical polarization ofsaid waves lying in a plane includ ng said linear slot and 'thelongitudinal aXis of fsa'id extension, 'and a plurality -bf partitions"extend ing transversely across the 4linear slot said outer member, saidpartitions being spaced apart `by intervals equalt'o small fraction of"the wavelength of the energy usefully radiated through said slo't andyacting 'to 'out foff leakage 'energy polarized planes parallel totheplanes of -said partitions.

i3. In combination, a parabolic reflector, fa wave guide extensionextending along the lt'us rectum yof the reflector, said vfave fgu-ld'eeli/tension includ-ing a linearly slotted outer member la'nda coaxialhelically slotted rotatable inner meurber, the aperture formed by theintersection "of said slots facing said reector and constituting aprimary antenna, means for rotating said inner member 'to cause saidaperture to move at a uniform 'speed repeatedly and inthe same directionacross the focus of said reflector, and means disposed along the linearslot of said outer member adapted to permit the passage ofelectromagnetic wave energy by way of said aperture and to discriminateagainst the passage of energy 5 through other parts of the linear slot.

14. In combination, a parabolic reector and a Wave guide extensionhaving a linearly slotted portion mounted in xed relation to each other,a helically slotted rotatable element coaxially located Within saidlinearly slotted portion, means for rotating said element to cause anaperture formed by the intersection of the slots to move repeatedly andin the same direction across the focus of said reflector, and meansdisposed along the linear slot vadapted to prevent radiation of energydue to leakage along said slot and permit radiation of energy passingthrough said aperture.

CARL B. H. FELDMAN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,828,705 Kolster Oct. 20, 1931 1,932,469 Leib Oct. 31, 19331,934,078 Ludenia Nov. 7, 1933 2,075,808 Fliess Apr. 6, 1937 2,156,653Illberg May 2, 1939 2,206,923 Southworth July 9, 1940 2,238,770 BlumleinApr. 15, 1941 2,429,601 Biskeborn et a1. Oct. 28', 1947 2,436,380 CutlerFeb. 24, 1948 2,446,436 Rouault Aug. 3, 1948

